Bilateral filter for predicted video data

ABSTRACT

A device for coding video data includes a memory configured to store video data; and one or more processors comprising circuitry and configured to generate a prediction block for a current block of video data; apply a bilateral filter to the prediction block to generate a filtered prediction block for the current block, wherein to apply the bilateral filter, the processor is configured to determine weighting values to apply to neighboring pixels to a current pixel of the prediction block to be filtered according to values of the neighboring pixels; and code the current block using the filtered prediction block.

This application claims the benefit of U.S. Provisional Application No.62/656,872, filed Apr. 12, 2018, the entire contents of which are herebyincorporated by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard, ITU-TH.265/High Efficiency Video Coding (HEVC), and extensions of suchstandards. The video devices may transmit, receive, encode, decode,and/or store digital video information more efficiently by implementingsuch video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for bilateral filteringthat may be used during a prediction stage of video coding (encoding ordecoding). These techniques may be applied by any existing video codec,such as codecs according to ITU-T H.265/High Efficiency Video Coding(HEVC), or may be applied by future video codecs. These techniques mayoffer efficient coding tools in future video coding standards.

In one example, a method of coding video data includes generating aprediction block for a current block of video data; applying a bilateralfilter to the prediction block to generate a filtered prediction blockfor the current block, wherein applying the bilateral filter comprisesdetermining weighting values to apply to neighboring pixels to a currentpixel of the prediction block to be filtered according to values of theneighboring pixels; and coding the current block using the filteredprediction block.

In another example, a device for coding video data includes a memoryconfigured to store video data; and one or more processors comprisingcircuitry and configured to generate a prediction block for a currentblock of video data; apply a bilateral filter to the prediction block togenerate a filtered prediction block for the current block, wherein toapply the bilateral filter, the processor is configured to determineweighting values to apply to neighboring pixels to a current pixel ofthe prediction block to be filtered according to values of theneighboring pixels; and code the current block using the filteredprediction block.

In another example, a device for coding video data includes means forgenerating a prediction block for a current block of video data; meansfor applying a bilateral filter to the prediction block to generate afiltered prediction block for the current block, wherein the means forapplying the bilateral filter comprises means for determining weightingvalues to apply to neighboring pixels to a current pixel of theprediction block to be filtered according to values of the neighboringpixels; and means for coding the current block using the filteredprediction block.

In another example, a computer-readable storage medium has storedthereon instructions that, when executed, cause one or more processorsto generate a prediction block for a current block of video data; applya bilateral filter to the prediction block to generate a filteredprediction block for the current block, wherein the instructions thatcause the processor to apply the bilateral filter comprise instructionsthat cause the processor to determine weighting values to apply toneighboring pixels to a current pixel of the prediction block to befiltered according to values of the neighboring pixels; and code thecurrent block using the filtered prediction block.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example codingtree unit (CTU) and a corresponding quadtree data structure.

FIG. 3 is a block diagram illustrating an example HEVC decoder.

FIGS. 4A-4D are conceptual diagrams illustrating respective directionalpatterns for edge offset (EO) sample classification.

FIG. 5 is a conceptual diagram illustrating an example sample and itsneighboring four samples utilized in a bilateral filtering process.

FIG. 6 is a conceptual diagram illustrating an example sample and itsneighboring four samples utilized in bilateral filtering process.

FIG. 7 is a conceptual diagram illustrating an example sample andneighboring samples used in division-free bilateral filtering.

FIG. 8 is a conceptual diagram of one sample and its neighboring samplesto be used in bilateral filtering.

FIGS. 9A and 9B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 10 is a block diagram illustrating an example video encoder thatmay perform the techniques of this disclosure.

FIG. 11 is a block diagram illustrating an example video decoder thatmay perform the techniques of this disclosure.

FIG. 12 is a flowchart illustrating an example method for encoding acurrent block according to the techniques of this disclosure.

FIG. 13 is a flowchart illustrating an example method for decoding acurrent block of video data according to the techniques of thisdisclosure.

DETAILED DESCRIPTION

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multi-view Video Coding (MVC) extensions. Inaddition, a new video coding standard, namely High Efficiency VideoCoding (HEVC) or ITU-T H.265, including its range extension, multiviewextension (MV-HEVC) and scalable extension (SHVC), has recently beendeveloped by the Joint Collaboration Team on Video Coding (JCT-VC) aswell as Joint Collaboration Team on 3D Video Coding ExtensionDevelopment (JCT-3V) of ITU-T Video Coding Experts Group (VCEG) andISO/IEC Motion Picture Experts Group (MPEG). An HEVC draftspecification, referred to as “HEVC WD” hereinafter, is described inWang et al., “High Efficiency Video Coding (HEVC) Defect Report,” JointCollaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 andISO/IEC JTC 1/SC 29/WG 11, 14^(th) Meeting: Vienna, AT, 25 Jul. to 2Aug. 2013, Document JCTVC-N1003 v1, available atphenix.int-evry.fr/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1003-v1.zip.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) are now studyingthe potential need for standardization of future video coding technologywith a compression capability that significantly exceeds that of thecurrent HEVC standard (including its current extensions and near-termextensions for screen content coding and high-dynamic-range coding). Thegroups are working together on this exploration activity in a jointcollaboration effort known as the Joint Video Exploration Team (JVET) toevaluate compression technology designs proposed by their experts inthis area. The JVET first met during 19-21 Oct. 2015. A version ofreference software, i.e., Joint Exploration Model 7 (JEM 7) is availableat jvet.hhi.fraunhofer.de/svn/svn_HMJEMSoftware/tags/HM-16.6-JEM-7.0/. Adescription of Joint Exploration Test Model 7 (JEM7) is provided in Chenet al., “Algorithm Description of Joint Exploration Test Model 7 (JEM7),” Joint Video Exploration Team (JVET) of ITU-T SG 16 WP 3 and ISO/IECJTC 1/SC 29/WG 11, 7^(th) Meeting: Torino, IT, 13-21 Jul. 2017, DocumentJVET-G1001-v1, available atphenix.it-sudparis.eu/jvet/doc_end_user/current_document.php?id=3286.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,uncoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch smartphones, televisions, cameras, display devices, digital mediaplayers, video gaming consoles, video streaming device, or the like. Insome cases, source device 102 and destination device 116 may be equippedfor wireless communication, and thus may be referred to as wirelesscommunication devices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for bilateralfiltering of prediction blocks. Thus, source device 102 represents anexample of a video encoding device, while destination device 116represents an example of a video decoding device. In other examples, asource device and a destination device may include other components orarrangements. For example, source device 102 may receive video data froman external video source, such as an external camera. Likewise,destination device 116 may interface with an external display device,rather than including an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forbilateral filtering of prediction blocks. Source device 102 anddestination device 116 are merely examples of such coding devices inwhich source device 102 generates coded video data for transmission todestination device 116. This disclosure refers to a “coding” device as adevice that performs coding (encoding and/or decoding) of data. Thus,video encoder 200 and video decoder 300 represent examples of codingdevices, in particular, a video encoder and a video decoder,respectively. In some examples, devices 102, 116 may operate in asubstantially symmetrical manner such that each of devices 102, 116include video encoding and decoding components. Hence, system 100 maysupport one-way or two-way video transmission between video devices 102,116, e.g., for video streaming, video playback, video broadcasting, orvideo telephony.

In general, video source 104 represents a source of video data (i.e.,raw, uncoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some example, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although shown separately from video encoder 200 and videodecoder 300 in this example, it should be understood that video encoder200 and video decoder 300 may also include internal memories forfunctionally similar or equivalent purposes. Furthermore, memories 106,120 may store encoded video data, e.g., output from video encoder 200and input to video decoder 300. In some examples, portions of memories106, 120 may be allocated as one or more video buffers, e.g., to storeraw, decoded, and/or encoded video data.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may modulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 116. Similarly, destination device 116may access encoded data from storage device 116 via input interface 122.Storage device 116 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video generated by source device 102. Destination device 116may access stored video data from file server 114 via streaming ordownload. File server 114 may be any type of server device capable ofstoring encoded video data and transmitting that encoded video data tothe destination device 116. File server 114 may represent a web server(e.g., for a website), a File Transfer Protocol (FTP) server, a contentdelivery network device, or a network attached storage (NAS) device.Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on file server 114. File server 114 and input interface 122 maybe configured to operate according to a streaming transmission protocol,a download transmission protocol, or a combination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receiver, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., storage device 112,file server 114, or the like). The encoded video bitstreamcomputer-readable medium 110 may include signaling information definedby video encoder 200, which is also used by video decoder 300, such assyntax elements having values that describe characteristics and/orprocessing of video blocks or other coded units (e.g., slices, pictures,groups of pictures, sequences, or the like). Display device 118 displaysdecoded pictures of the decoded video data to a user. Display device 118may represent any of a variety of display devices such as a cathode raytube (CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM). The techniques of this disclosure, however, are not limitedto any particular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to JEM. According to JEM, a video coder(such as video encoder 200) partitions a picture into a plurality ofcoding tree units (CTUs). Video encoder 200 may partition a CTUaccording to a tree structure, such as a quadtree-binary tree (QTBT)structure. The QTBT structure of JEM removes the concepts of multiplepartition types, such as the separation between CUs, PUs, and TUs ofHEVC. A QTBT structure of JEM includes two levels: a first levelpartitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT structure to represent each of the luminance and chrominancecomponents, while in other examples, video encoder 200 and video decoder300 may use two or more QTBT structures, such as one QTBT structure forthe luminance component and another QTBT structure for both chrominancecomponents (or two QTBT structures for respective chrominancecomponents).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning according to JEM, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

JEM also provides an affine motion compensation mode, which may beconsidered an inter-prediction mode. In affine motion compensation mode,video encoder 200 may determine two or more motion vectors thatrepresent non-translational motion, such as zoom in or out, rotation,perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. JEM providessixty-seven intra-prediction modes, including various directional modes,as well as planar mode and DC mode. In general, video encoder 200selects an intra-prediction mode that describes neighboring samples to acurrent block (e.g., a block of a CU) from which to predict samples ofthe current block. Such samples may generally be above, above and to theleft, or to the left of the current block in the same picture as thecurrent block, assuming video encoder 200 codes CTUs and CUs in rasterscan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

In accordance with the techniques of this disclosure, as discussed ingreater detail below, video encoder 200 and video decoder 300 may applya bilateral filter to a prediction block. That is, video encoder 200 andvideo decoder 300 may apply the bilateral filter to each pixel (orsample) of the prediction block. The bilateral filter may indicate a setof neighboring pixels to the current pixel of the prediction block towhich to apply weighting values. The neighboring pixels may include oneor more horizontally neighboring pixels and/or one or more verticallyneighboring pixels, e.g., as shown in and discussed with respect toFIGS. 4-8 below. Moreover, video encoder 200 and video decoder 300 maydetermine the weighting values based on the values of the neighboringpixels themselves. Video encoder 200 and video decoder 300 may thusdetermine the weighting values and apply the weighting values to theneighboring pixel values to filter the current pixel, thereby updatingthe value of the current pixel.

Following prediction, such as intra-prediction or inter-prediction of ablock, and filtering of the resulting prediction blocks, video encoder200 may calculate residual data for the block. The residual data, suchas a residual block, represents sample by sample differences between theblock and a prediction block for the block, formed using thecorresponding prediction mode. Video encoder 200 may apply one or moretransforms to the residual block, to produce transformed data in atransform domain instead of the sample domain. For example, videoencoder 200 may apply a discrete cosine transform (DCT), an integertransform, a wavelet transform, or a conceptually similar transform toresidual video data. Additionally, video encoder 200 may apply asecondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of thecoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the vector and to place lowerenergy (and therefore higher frequency) transform coefficients at theback of the vector. In some examples, video encoder 200 may utilize apredefined scan order to scan the quantized transform coefficients toproduce a serialized vector, and then entropy encode the quantizedtransform coefficients of the vector. In other examples, video encoder200 may perform an adaptive scan. After scanning the quantized transformcoefficients to form the one-dimensional vector, video encoder 200 mayentropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information of apicture into CTUs, and partitioning of each CTU according to acorresponding partition structure, such as a QTBT structure, to defineCUs of the CTU. The syntax elements may further define prediction andresidual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values syntax elements and/or other data used to decodeencoded video data. That is, video encoder 200 may signal values forsyntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagrams illustrating an example codingtree unit (CTU) 130 and a corresponding quadtree data structure 132.HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). In HEVC, the largest coding unitin a slice is called a coding tree block (CTB) or coding tree unit(CTU). A CTB contains a quad-tree, the nodes of which are coding units.According to HEVC, a video coder (such as video encoder 200) partitionsa coding tree unit (CTU) into CUs according to a quadtree structure.That is, the video coder partitions CTUs and CUs into four equal,non-overlapping squares, and each node of the quadtree has either zeroor four child nodes. Nodes without child nodes may be referred to as“leaf nodes,” and CUs of such leaf nodes may include one or more PUsand/or one or more TUs. The video coder may further partition PUs andTUs. For example, in HEVC, a residual quadtree (RQT) representspartitioning of TUs. In HEVC, PUs represent inter-prediction data, whileTUs represent residual data. CUs that are intra-predicted includeintra-prediction information, such as an intra-mode indication.

In HEVC, blocks specified as luma and chroma CTBs can be directly usedas CBs or can be further partitioned into multiple CBs. Partitioning isachieved using tree structures. The tree partitioning in HEVC isgenerally applied simultaneously to both luma and chroma, althoughexceptions apply when certain minimum sizes are reached for chroma.

The CTU of HEVC contains a quadtree syntax that allows for splitting theCBs to a selected appropriate size based on the signal characteristicsof the region that is covered by the CTB. The quadtree splitting processcan be iterated until the size for a luma CB reaches a minimum allowedluma CB size that is selected by the encoder using syntax in the SPSand, per HEVC, is always 8×8 or larger (in units of luma samples).

The boundaries of the picture are defined, in HEVC, in units of theminimum allowed luma CB size. As a result, at the right and bottom edgesof the picture, some CTUs may cover regions that are partly outside theboundaries of the picture. This condition is detected by the decoder(e.g., video decoder 300), and the CTU quadtree is implicitly split asnecessary to reduce the CB size to the point where the entire CB willfit into the picture.

FIG. 3 is a block diagram illustrating an example HEVC decoder. HEVCemploys two in-loop filters, including a de-blocking filter (DBF) and asample adaptive offset (SAO) filter, as shown in FIG. 3. The videodecoder of FIG. 3 may correspond to video decoder 300 (FIG. 1).

The DBF receives input including a reconstructed image after intra orinter prediction. The deblocking filter performs detection of theartifacts at the coded block boundaries and attenuates them by applyinga selected filter. Compared to the H.264/AVC deblocking filter, the HEVCdeblocking filter has lower computational complexity and better parallelprocessing capabilities, while still achieving significant reduction ofthe visual artifacts.

The SAO filter receives the reconstructed image after invokingdeblocking filtering. The concept of SAO is to reduce mean sampledistortion of a region by first classifying the region samples intomultiple categories with a selected classifier, obtaining an offset foreach category, and then adding the offset to each sample of thecategory, where the classifier index and the offsets of the region arecoded in the bitstream. In HEVC, the region (the unit for SAO parameterssignaling) is defined to be a coding tree unit (CTU). Two SAO types thatcan satisfy the requirements of low complexity are adopted in HEVC: edgeoffset (EO) and band offset (BO). An index of SAO type may be coded(which may be in the range of [0, 2]).

FIGS. 4A-4D are conceptual diagrams illustrating respective directionalpatterns for edge offset (EO) sample classification. FIG. 4A depictshorizontal (EO class=0), FIG. 4B depicts vertical (EO class=1), FIG. 4Cdepicts 135 degree diagonal (EO class=2), and FIG. 4D depicts 45 degreediagonal (EO class=3).

For EO, the sample classification is based on a comparison betweencurrent samples and neighboring samples according to 1-D directionalpatterns: horizontal, vertical, 135° diagonal, and 45° diagonal.According to the selected EO pattern, five categories denoted by edgeIdxin Table I are further defined. For edgeIdx equal to 0-3, the magnitudeof an offset may be signaled while the sign flag is implicitly coded,i.e., negative offset for edgeIdx equal to 0 or 1 and positive offsetfor edgeIdx equal to 2 or 3. For edgeIdx equal to 4, the offset isalways set to 0 which means no operation is required for this case.

TABLE I Category (edgeIdx) Condition 0 c < a && c < b 1 (c < a && c ==b) ∥ (c == a && c < b) 2 (c > a && c == b) ∥ (c == a && c > b) 3 c > a&& c > b 4 None of the above

For BO, the sample classification is based on sample values. Each colorcomponent may have its own SAO parameters. BO implies one offset isadded to all samples of the same band. The sample value range is equallydivided into 32 bands. For 8-bit samples ranging from 0 to 255, thewidth of a band is 8, and sample values from 8k to 8k+7 belong to bandk, where k ranges from 0 to 31. The average difference between theoriginal samples and reconstructed samples in a band (i.e., offset of aband) is signaled to the decoder. There is no constraint on offsetsigns. Only offsets of four consecutive bands and the starting bandposition are signaled to the decoder.

To reduce side information, multiple CTUs can be merged together (eithercopying the parameters from an above CTU (through settingsao_merge_left_flag equal to 1) or left CTU (through settingsao_merge_up_flag equal to 1) to share SAO parameters.

In addition to the modified DB and HEVC SAO methods, JEM includesanother filtering method, called Geometry transformation-based AdaptiveLoop Filtering (GALF). GALF aims improve the coding efficiency of ALFstudied in HEVC stage by introducing several new aspects. ALF is aimingto minimize the mean square error between original samples and decodedsamples by using Wiener-based adaptive filter. Samples in a picture areclassified into multiple categories and the samples in each category arethen filtered with their associated adaptive filter. The filtercoefficients may be signaled or inherited to optimize the tradeoffbetween the mean square error and the overhead. In this paper, aGeometry transformation-based ALF (GALF) scheme is proposed to furtherimprove the performance of ALF, which introduces geometrictransformations, such as rotation, diagonal and vertical flip, to beapplied to the samples in filter support region depending on theorientation of the gradient of the reconstructed samples before ALF.Input to ALF/GALF may be the reconstructed image after invoking SAO.

In M. Karczewicz, L. Zhang, W.-J. Chien, X. Li, “EE2.5: Improvements onadaptive loop filter”, Exploration Team (JVET) of ITU-T SG 16 WP 3 andISO/IEC JTC 1/SC 29/WG 11, Doc. JVET-B0060, 2nd Meeting: San Diego, USA,20 Feb.-26 Feb. 2016 and M. Karczewicz, L. Zhang, W.-J. Chien, X. Li,“EE2.5: Improvements on adaptive loop filter”, Exploration Team (JVET)of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, Doc. JVET-00038,3^(rd) Meeting: Geneva, CH, 26 May-1 Jun. 2016, the Geometrictransformations-based ALF (GALF) is proposed, and has been adopted tothe most recent version of JEM, i.e., JEM3.0. In GALF, theclassification is modified with the diagonal gradients taken intoconsideration and geometric transformations could be applied to filtercoefficients. Each 2×2 block is categorized into one out of 25 classesbased on its directionality and quantized value of activity. The detailsare described below.

Bilateral filtering was formerly proposed in C. Tomasi and R. Manduchi,“Bilateral filtering for gray and color images”, in Proc. of IEEE ICCV,Bombay, India, January 1998, to avoid undesirable over-smoothing forpixels in the edge. The main idea of bilateral filtering is theweighting of neighboring samples takes the pixel values themselves intoaccount to weight more those pixels with similar luminance orchrominance values. A sample located at (i, j), will be filtered usingits neighboring sample (k, l). The weight ω(i,j,k,l) is the weightassigned for sample (k, l) to filter the sample (i, j), and it isdefined as:

$\begin{matrix}{{\omega\left( {i,j,k,l} \right)} = e^{({{- \frac{{({i - k})}^{2} + {({j - l})}^{2}}{2\sigma_{d}^{2}}} - \frac{{{{I{({i,j})}} - {I{({k,l})}}}}^{2}}{2\sigma_{r}^{2}}})}} & (1)\end{matrix}$

where I(i, j) and I(k, l) are the intensity value of samples (i, j) and(k,l) respectively. σ_(d) is the spatial parameter, and σ_(r) is therange parameter. The filtering process with the filtered sample valuedenoted by I_(D)(i,j) could be defined as:

$\begin{matrix}{{I_{D}\left( {i,j} \right)} = \frac{\sum_{k,l}{{I\left( {k,l} \right)}*{\omega\left( {i,j,k,l} \right)}}}{\sum_{k,l}{\omega\left( {i,j,k,l} \right)}}} & (2)\end{matrix}$

The properties (or strength) of the bilateral filter are controlled bythese two parameters. Samples located closer to the sample to befiltered, and samples having smaller intensity difference to the sampleto be filtered, will have larger weights than samples further away andwith larger intensity differences.

In Jacob Ström, Per Wennersten, Ying Wang, Kenneth Andersson, JonatanSamuelsson, “Bilateral filter after inverse transform,” JVET-D0069, 4thMeeting: Chengdu, CN, 15-21 Oct. 2016, each reconstructed sample in thetransform unit (TU) is filtered using its direct neighboringreconstructed samples only. The filter has a plus sign shaped filteraperture centered at the sample to be filtered, as depicted in FIG. 4.σ_d to be set based on the transform unit size (3), and σ_r to be setbased on the QP used for the current block (4).

$\begin{matrix}{\sigma_{d} = {0.92 - \frac{\min\left( {16,{\min\left( {{{TU}\mspace{14mu}{block}\mspace{14mu}{width}},{{TU}\mspace{14mu}{block}\mspace{14mu}{height}}} \right)}} \right)}{40}}} & (3) \\{\sigma_{r} = {\max\left( {\frac{\left( {{QP} - 17} \right)}{2},0.01} \right)}} & (4)\end{matrix}$

FIG. 5 is a conceptual diagram illustrating a sample and its neighboringfour samples utilized in a bilateral filtering process. In J. Ström, P.Wennersten, K. Andersson, J. Enhorn, “Bilateral filter strength based onprediction mode”, JVET-E0032, 5th Meeting: Geneva, CH, 12-20 Jan. 2017,to further reduce the coding loss under low delay configuration, thefilter strength is further designed to be dependent on the coded mode.For intra-coded blocks, the above equation (3) is still used. While forinter-coded blocks, the following equation is applied:

$\begin{matrix}{\sigma_{d} = {0.72 - \frac{\min\left( {8,{\min\left( {{{TU}\mspace{14mu}{block}\mspace{14mu}{width}},{{TU}\mspace{14mu}{block}\mspace{14mu}{height}}} \right)}} \right)}{40}}} & (5)\end{matrix}$

The different values for σ_(d) means that filter strength for interprediction blocks is relatively weaker compared to that of intraprediction blocks. Inter prediction blocks typically have less residualthan intra prediction blocks. Therefore, the bilateral filter isdesigned to filter the reconstruction of inter prediction blocks less.The output filtered sample value I_(D)(i,j) is calculated as:

$\begin{matrix}{{I_{F}\left( {i,j} \right)} = \frac{\sum_{k,l}{{I\left( {k,l} \right)}*{\omega\left( {i,j,k,l} \right)}}}{\sum_{k,l}{\omega\left( {i,j,k,l} \right)}}} & (6)\end{matrix}$

Due to the fact that the filter only touches the sample and its4-neighbours, this equation can be written as:

$\begin{matrix}{I_{F} = \frac{{I_{C}\omega_{C}} + {I_{L}\omega_{L}} + {I_{R}\omega_{R}} + {I_{A}\omega_{A}} + {I_{B}\omega_{B}}}{\omega_{C} + \omega_{L} + \omega_{R} + \omega_{A} + \omega_{B}}} & (7)\end{matrix}$

where I_(C) is the intensity of the center sample, and I_(L), I_(R),I_(A) and I_(B) are the intensities for the left, right, above and belowsamples, respectively. Likewise, Ω_(C) is the weight for the centersample, and ω_(L), ω_(R), ω_(A) and ω_(B) are the corresponding weightsfor the neighbouring samples. The filter only uses samples within theblock for filtering—weights outside are set to 0.

In order to reduce the number of calculations, the bilateral filter inthe JEM has been implemented using a look-up-table (LUT). For every QP,there is a one-dimensional LUT for the values ω_(L), ω_(B), ω_(A) andω_(B) where the value

$\begin{matrix}{\omega_{other} = {{round}\left( {65*e^{({{- \frac{1}{2*0.82^{2}}} - \frac{{{I - I_{C}}}^{2}}{2\sigma_{r}^{2}}})}} \right)}} & (8)\end{matrix}$

is stored, where σ_(r) ² is calculated from (4) depending upon QP. Sinceσ_(d)=0.92−4/40=0.82 in the LUT, it can be used directly for the intraM×N with minimum(M, N) equal to 4 case with a center weight ω_(C) of 65,which represents 1.0. For the other modes (i.e., intra M×N but minimum(M, N) unequal to 4, inter K×L blocks), we use the same LUT, but insteaduse a center weight of:

$\begin{matrix}{{\omega_{C} = {{round}\left( {65*\frac{e^{- \frac{1}{2*0.82^{2}}}}{e^{- \frac{1}{2*\sigma_{d}^{2}}}}} \right)}},} & (9)\end{matrix}$

where σ_(d) is obtained by (3) or (5). The final filtered value iscalculated as:

$\begin{matrix}{I_{F} = {{floor}\left( \frac{\begin{matrix}{{I_{C}\omega_{C}} + {I_{L}\omega_{L}} + {I_{R}\omega_{R}} + {I_{A}\omega_{A}} + {I_{B}\omega_{B}} +} \\\left( {\left( {\omega_{C} + \omega_{L} + \omega_{R} + \omega_{A} + \omega_{B}} \right)\operatorname{>>}1} \right)\end{matrix}}{\omega_{C} + \omega_{L} + \omega_{R} + \omega_{A} + \omega_{B}} \right)}} & (10)\end{matrix}$

where the division used is integer division and the term(ω_(C)+ω_(L)+ω_(B)+ω_(A)+ω_(B))>>1 is added to get correct rounding.

In the JEM reference software, the division operation in Equation 10 isreplaced by LUT, multiplication and shift operations. To reduce the sizeof the numerator and denominator, Equation 10 is further refined to:

$\begin{matrix}{I_{F} = {I_{C} + \frac{{\omega_{L}\left( {I_{L} - I_{C}} \right)} + {\omega_{R}\left( {I_{R} - I_{C}} \right)} + {\omega_{A}\left( {I_{A} - I_{C}} \right)} + {\omega_{B}\left( {I_{B} - I_{C}} \right)}}{\omega_{C} + \omega_{L} + \omega_{R} + \omega_{A} + \omega_{B}}}} & (11)\end{matrix}$

In the JEM reference software, Equation 11 is implemented in a way thatthe division could be implemented by two look-up tables, and (11) couldbe rewriten as:I _(F) =I_(C)sign(PixelDeltaSum)*((sign(PixelDeltaSum)*PixelDeltaSum+o)*LUT(sumWeights)>>(14+DivShift(sumWeights)))  (12)PixelDeltaSum=(ω_(L)(I _(L) −I _(C))+ω_(R)(I _(R) −I _(C))+ω_(A)(I _(A)−I _(C))+ω_(B)(I _(B) −I _(C))sumWeights=⋅_(C)+ω_(L)+ω_(R)+ω_(A)+ω_(B)o=PixelDeltaSum+sign(PixelDeltaSum)sign(x)=x>=0?1: −1;

The two look-up tables are the look-up table LUT to get an approximatedvalue for each 1/x (x is an positive interger value) after shifting, anda look-up table DivShift to define the additional shift value for inputx. J. Ström, P. Wennersten, K. Andersson, J. Enhorn, “EE2-JVET related:Division-free bilateral filter”, JVET-F0096, 6th Meeting: Hobart, CH, 31Mar.-7 Apr. 2017 describes further details of this.

The filter is turned off if QP<18 or if the block is of inter type andthe block dimensions are 16×16 or larger. It is noted that the proposedbilateral filtering method is only applied to luma blocks with at leastone non-zero coefficients. For chroma blocks and luma blocks with allzero coefficients, the bilateral filtering method is always disabled.

FIG. 6 is a conceptual diagram illustrating an example sample and itsneighboring four samples utilized in bilateral filtering process. FIG. 6depicts an example of a current sample at the left boundary (i.e., leftcolumn), for which only neighboring samples within current TU are usedto filter the current sample. Similar concepts apply to samples at thetop of the TU boundary.

U.S. Provisional Application No. 62/528,912, filed Jul. 5, 2017, andU.S. Provisional Application No. 62/556,614, filed Sep. 11, 2017,describe division-free bilateral filtering (DFBil) methods. For onesample to be filtered, the filtering process could be defined as:

$I_{F} = {I_{C} + {\sum\limits_{i = 1}^{N}{{W\left( {{abs}\left( {I_{i} - I_{c}} \right)} \right)}*\left( {I_{i} - I_{c}} \right)}}}$where I_(C) is the intensity of the current sample and I_(F) is themodified intensity of the current sample after performing DFBil, I_(i)and W(abs(I_(i)−I_(c))) are the intensity and weighting parameter forthe i-th neighboring sample, respectively.

w_(i) = Dis_(i) * Rang_(i)${Rang}_{i} = e^{({- \frac{{{I_{i} - I_{c}}}^{2}}{2\sigma_{r}^{2}}})}$${Dis}_{i} = \frac{{TempD}_{i}}{1 + {\sum\limits_{j = 1}^{N}{TempD}_{j}}}$${TempD}_{i} = e^{({- \frac{10^{4}*{{sqrt}{({{({i - k})}^{2} + {({j - l})}^{2}})}}}{2\sigma_{d}^{2}}})}$σ_(r) = (QP − min  DFBilQP + 2 * Index_(r) − 2 * (RCandNum/2)) * 2σ_(d) = DCandidateList[Index_(d)]

where minDFBilQP indicates the minimum QP that could apply DFBil, e.g.,the minimum QP may be set to 17. Indexd and Indexr may be signaled perquad-tree partition.

FIG. 7 is a conceptual diagram illustrating an example sample andneighboring samples used in DFBil as discussed above.

This disclosure recognizes that in the design of bilateral filtering,non-division bilateral filter techniques may encounter certain problems.For example, such techniques are applied directly to the reconstructedblock or after the whole slice is reconstructed. This mainly helps thespatial neighboring block of the block that was reconstructed if thereconstructed block was coded with intra mode, or for blocks in thefollowing frames. If those filters could be applied to prediction signal(e.g., the prediction block that is used to reconstruct the currentblock as part of decoding or used to determine a residual block as partof encoding), additional coding gain may be obtained since it may helpfor reducing the prediction errors.

FIGS. 9A and 9B are conceptual diagram illustrating an example quadtreebinary tree (QTBT) structure 134, and a corresponding coding tree unit(CTU) 136. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, since quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 134(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 134 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 134.

In general, CTU 136 of FIG. 9B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 134 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 136 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 134 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), they can be furtherpartitioned by respective binary trees. The binary tree splitting of onenode can be iterated until the nodes resulting from the split reach theminimum allowed binary tree leaf node size (MinBTSize) or the maximumallowed binary tree depth (MaxBTDepth). The example of QTBT structure134 represents such nodes as having dashed lines for branches. Thebinary tree leaf node is referred to as a coding unit (CU), which isused for prediction (e.g., intra-picture or inter-picture prediction)and transform, without any further partitioning. As discussed above, CUsmay also be referred to as “video blocks” or “blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If theleaf quadtree node is 128×128, it will not be further split by thebinary tree, since the size exceeds the MaxBTSize (i.e., 64×64, in thisexample). Otherwise, the leaf quadtree node will be further partitionedby the binary tree. Therefore, the quadtree leaf node is also the rootnode for the binary tree and has the binary tree depth as 0. When thebinary tree depth reaches MaxBTDepth (4, in this example), no furthersplitting is permitted. When the binary tree node has width equal toMinBTSize (4, in this example), it implies no further horizontalsplitting is permitted. Similarly, a binary tree node having a heightequal to MinBTSize implies no further vertical splitting is permittedfor that binary tree node. As noted above, leaf nodes of the binary treeare referred to as CUs, and are further processed according toprediction and transform without further partitioning.

Referring again to FIG. 1, video encoder 200 and video decoder 300 maybe configured to perform any or all of the techniques of thisdisclosure, in any combination. Such techniques include bilateralfiltering techniques. However, these techniques may generally be appliednot only to bilateral filters and division-free bilateral filters, butto any other filters that may be applied to a prediction signal.

Video encoder 200 and video decoder 300 may apply a bilateral filter(including a non-local bilateral filter) to a prediction block of acurrent block. In one example, even for bi-prediction (wherein twotemporary prediction blocks may be generated based on motion informationfor each of the two prediction directions) or multi-hypothesis, anon-local bilateral filter may be applied only once, that is, onlyapplied to the final prediction block. Alternatively, video encoder 200and/or video decoder 300 may apply a bilateral filter to each of thetemporary prediction blocks, regardless of whether the temporaryprediction blocks are conventional bi-prediction blocks or blocks codedwith multi-hypothesis (e.g., JVET-J0041). Therefore, multiple iterationsof bilateral filtering may be applied. Alternatively, formulti-hypothesis coded block (that is, blocks that may be predicted frommultiple reference blocks), video encoder 200 and video decoder 300 mayapply a bilateral filter only twice, where the prediction blocks may befirstly grouped to generate another temporary block. In one example,which of the prediction blocks may be grouped may depend on the POCdistance between the two reference pictures. Video encoder 200 and videodecoder 300 may generate prediction blocks with any kind of prediction,such as inter-prediction, intra-prediction, intra-block copy,cross-component linear model prediction (like LM), inter-layerprediction in scalable video coding, inter-view prediction in 3D-videocoding, or any combination such as weighted sum of two or more kinds ofprediction.

FIG. 8 is a conceptual diagram of one sample and its neighboring samplesto be used in bilateral filtering. When bilateral filter is applied toprediction block as mentioned above, the parameters for bilateralfiltering may be signaled. That is, video encoder 200 may signal (e.g.,encode and output) the bilateral filtering parameters, and video decoder300 may receive, decode, and interpret the bilateral filteringparameters. A flag may be further signaled per CU/LCU to indicatewhether the filtering applied to prediction block(s) is enabled or not.For each temporary prediction block or each grouped temporary predictionblock, to which a bilateral filter is applied, a flag may be signaled.The signaling method for parameters (e.g., weights) may be as describedin, e.g., U.S. Provisional Application No. 62/528,912, filed Jul. 5,2017, and U.S. Provisional Application No. 62/556,614, filed Sep. 11,2017. Alternatively, not all of the weights associated with neighborsamples may be required to be signaled. Instead, for center positions,the weight may be derived on-the-fly without being signaled. An exampleis depicted in FIG. 8. Alternatively, the parameters may be derivedon-the-fly without being signaled. Alternatively, whether to signal theparameters (or partial of the parameters) may depend on the codedinformation, such as if it is AMVP mode, parameters may be signaled; ifit is merge mode, parameters may be inherited from the neighboring blockwherein the motion information is obtained from. Alternatively, even forthe merge mode, one flag to indicate whether to inherit or signalparameters may be further signaled.

Video encoder 200 and video decoder 300 may be configured to apply thetechniques of this disclosure to certain color components only (e.g.,luma only), to certain block sizes only (e.g., blocks smaller than agiven size), and/or to certain block shapes only (e.g., square ornon-square blocks). The proposed methods may be disallowed without beingsignaled for certain coded modes (such as DC/Planar intra predictionmodes, skip mode, quantization parameters). The proposed methods may bedisallowed without being signaled for certain blocks with no non-zerocoefficients, quite a few number of non-zero coefficients, or all of theabsolute values of transform coefficients being less than a threshold.

When bilateral filter or other kinds of filter is applied multiple timesto the prediction block(s), instead of using average, video encoder 200and video decoder 300 may use different linear combination of multiplefiltered temporary prediction blocks to generate the final predictionblock. In one example, for bi-prediction, instead of using average oftwo filtered temporary prediction blocks to generate the finalprediction block, video encoder 200 and video decoder 300 may use(M*P0+N*P1)/(M+N), where Pi denotes the filtered temporary predictionblock from reference picture list i (i being 0 or 1), M and N denote thelinear weight for each of the filtered temporary prediction block.

When filters (such as bilateral filter) could be applied to predictionblock(s), the following may apply. In one example, one or multipledefault sets of filter parameters may be pre-defined or signaled inSPS/PPS/VPS/slice header. Alternatively, the difference between thedefault set of filter parameters and the real filter may be furthersignaled at block-level (such as CU/LCU/region with size smaller than aslice/tile/wavefront).

There may be some constraints of how to apply the filtering on theprediction blocks. For example, blocks larger or smaller than athreshold cannot apply this filter. In another example, blocks with aspecific prediction type, such as Illumination Compensation (IC),affine, or Alternative Temporal Motion Vector Prediction (ATMVP) cannotapply the filter.

FIG. 10 is a block diagram illustrating an example video encoder 200that may perform the techniques of this disclosure. FIG. 10 is providedfor purposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 video coding standard in development. However,the techniques of this disclosure are not limited to these video codingstandards, and are applicable generally to video encoding and decoding.

In the example of FIG. 10, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 10 are illustrated to assist withunderstanding the operations performed by video encoder 200. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that canprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, the one or more of the units maybe distinct circuit blocks (fixed-function or programmable), and in someexamples, the one or more units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theobject code of the software that video encoder 200 receives andexecutes, or another memory within video encoder 200 (not shown) maystore such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 210 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to filter unit216. In accordance with the techniques of this disclosure, filter unit216 applies a bilateral filter to the prediction block to generate afiltered prediction block. As discussed above, filter unit 216 maydetermine weighting values to apply to neighboring pixels (i.e.,samples) to a current pixel of the prediction block to be filteredaccording to the values of the neighboring pixels. The weighting may behigher for pixels with similar luminance or chrominance values to thevalue of the current pixel. Likewise, the weighting may be higher forpixels that are closer to the current pixel than pixels that are furtherfrom the current pixel.

Filter unit 216 provides the filtered prediction unit to residualgeneration unit 204. Residual generation unit 204 receives a raw,uncoded version of the current block from video data memory 230 and theprediction block from mode selection unit 202. Residual generation unit204 calculates sample-by-sample differences between the current blockand the prediction block. The resulting sample-by-sample differencesdefine a residual block for the current block. In some examples,residual generation unit 204 may also determine differences betweensample values in the residual block to generate a residual block usingresidual differential pulse code modulation (RDPCM). In some examples,residual generation unit 204 may be formed using one or more subtractorcircuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder20 and video decoder 30 may also support asymmetric partitioning for PUsizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit does not further partition a CUinto PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 120 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as fewexamples, mode selection unit 202, via respective units associated withthe coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block. Thus,

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the coefficient blocks associated withthe current block by adjusting the QP value associated with the CU.Quantization may introduce loss of information, and thus, quantizedtransform coefficients may have lower precision than the originaltransform coefficients produced by transform processing unit 206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from the filteredprediction block generated by mode selection unit 202 and filter unit216 to produce the reconstructed block. Additional filtering may beperformed, such as an in-loop deblocking filter to address blockinessartifacts, although this filter is not shown in FIG. 10.

Video encoder 200 stores reconstructed (and potentially filtered) blocksin DPB 218. Motion estimation unit 222 and motion compensation unit 224may retrieve a reference picture from DPB 218, formed from thereconstructed blocks, to inter-predict blocks of subsequently encodedpictures. In addition, intra-prediction unit 226 may use reconstructedblocks in DPB 218 of a current picture to intra-predict other blocks inthe current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding blocks andthe chroma coding blocks.

In this manner, video encoder 200 represents an example of a device forcoding (namely, encoding) video data including a memory configured tostore video data; and one or more processors comprising circuitry andconfigured to generate a prediction block for a current block of videodata; apply a bilateral filter to the prediction block to generate afiltered prediction block for the current block, wherein to apply thebilateral filter, the processor is configured to determine weightingvalues to apply to neighboring pixels to a current pixel of theprediction block to be filtered according to values of the neighboringpixels; and code the current block using the filtered prediction block.

FIG. 11 is a block diagram illustrating an example video decoder 300that may perform the techniques of this disclosure. FIG. 11 is providedfor purposes of explanation and is not limiting on the techniques asbroadly exemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 is describedaccording to the techniques of JEM and HEVC. However, the techniques ofthis disclosure may be performed by video coding devices that areconfigured to other video coding standards.

In the example of FIG. 11, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Prediction processing unit 304includes motion compensation unit 316 and intra-prediction unit 318.Prediction processing unit 304 may include addition units to performprediction in accordance with other prediction modes. As examples,prediction processing unit 304 may include a palette unit, anintra-block copy unit (which may form part of motion compensation unit318), an affine unit, a linear model (LM) unit, or the like. In otherexamples, video decoder 300 may include more, fewer, or differentfunctional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. CPB memory 320and DPB 314 may be provided by the same memory device or separate memorydevices. In various examples, CPB memory 320 may be on-chip with othercomponents of video decoder 300, or off-chip relative to thosecomponents.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to executed by processing circuitry of video decoder 300.

The various units shown in FIG. 11 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 10, fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, the one ormore of the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, the one or more units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 10).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 10).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Prediction processing unit 304 provides a prediction block to filterunit 312 to generate a filtered prediction block. In accordance with thetechniques of this disclosure, filter unit 312 applies a bilateralfilter to the prediction block to generate a filtered prediction block.As discussed above, filter unit 312 may determine weighting values toapply to neighboring pixels (i.e., samples) to a current pixel of theprediction block to be filtered according to the values of theneighboring pixels. The weighting may be higher for pixels with similarluminance or chrominance values to the value of the current pixel.Likewise, the weighting may be higher for pixels that are closer to thecurrent pixel than pixels that are further from the current pixel.

Filter unit 312 provides the filtered prediction block to reconstructionunit 310. Reconstruction unit 310 may reconstruct the current blockusing the filtered prediction block and the residual block. For example,reconstruction unit 310 may add samples of the residual block tocorresponding samples of the filtered prediction block to reconstructthe current block. Although not shown in FIG. 11, video decoder 300 mayfurther include an in-loop filter for filtering the reconstructedblocks, e.g., to remove blockiness artifacts. The in-loop filter mayfilter the output of reconstruction unit 310 and store the resultingfiltered blocks to DPB 314.

Video decoder 300 may store the reconstructed blocks in DPB 314. Asdiscussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures fromDPB for subsequent presentation on a display device, such as displaydevice 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a device forcoding (namely, decoding) video data including a memory configured tostore video data; and one or more processors comprising circuitry andconfigured to generate a prediction block for a current block of videodata; apply a bilateral filter to the prediction block to generate afiltered prediction block for the current block, wherein to apply thebilateral filter, the processor is configured to determine weightingvalues to apply to neighboring pixels to a current pixel of theprediction block to be filtered according to values of the neighboringpixels; and code the current block using the filtered prediction block.

FIG. 12 is a flowchart illustrating an example method for encoding acurrent block according to the techniques of this disclosure. Thecurrent block may comprise a current CU. Although described with respectto video encoder 200 (FIGS. 1 and 10), it should be understood thatother devices may be configured to perform a method similar to that ofFIG. 12.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. Filter unit 216 of video encoder 200 may applybilateral filtering to the prediction block (352) according to any orall of the techniques of this disclosure, as discussed above.

Video encoder 200 may then calculate a residual block for the currentblock (354). To calculate the residual block, video encoder 200 maycalculate a difference between the original, uncoded block and theprediction block for the current block. Video encoder 200 may thentransform and quantize coefficients of the residual block (356). Next,video encoder 200 may scan the quantized transform coefficients of theresidual block (358). During the scan, or following the scan, videoencoder 200 may entropy encode the coefficients (360). For example,video encoder 200 may encode the coefficients using CAVLC or CABAC.Video encoder 200 may then output the entropy coded data of the block(362).

In this manner, the method of FIG. 12 represents an example of a methodof coding (namely, encoding) video data including generating aprediction block for a current block of video data; applying a bilateralfilter to the prediction block to generate a filtered prediction blockfor the current block, wherein applying the bilateral filter comprisesdetermining weighting values to apply to neighboring pixels to a currentpixel of the prediction block to be filtered according to values of theneighboring pixels; and coding the current block using the filteredprediction block.

FIG. 13 is a flowchart illustrating an example method for decoding acurrent block of video data according to the techniques of thisdisclosure. The current block may comprise a current CU. Althoughdescribed with respect to video decoder 300 (FIGS. 1 and 11), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 13.

Video decoder 300 may receive entropy coded data for the current block,such as entropy coded prediction information and entropy coded data forcoefficients of a residual block corresponding to the current block(370). Video decoder 300 may entropy decode the entropy coded data todetermine prediction information for the current block and to reproducecoefficients of the residual block (372). Video decoder 300 may predictthe current block (374), e.g., using an intra- or inter-prediction modeas indicated by the prediction information for the current block, tocalculate a prediction block for the current block. Filter unit 312 ofvideo decoder 300 may then apply a bilateral filter to the predictionblock (376) according to any or all of the techniques of thisdisclosure, as discussed above. Video decoder 300 may then inverse scanthe reproduced coefficients (378), to create a block of quantizedtransform coefficients. Video decoder 300 may then inverse quantize andinverse transform the coefficients to produce a residual block (380).Video decoder 300 may ultimately decode the current block by combiningthe prediction block and the residual block (382).

In this manner, the method of FIG. 13 represents an example of a methodof coding (namely, decoding) video data including generating aprediction block for a current block of video data; applying a bilateralfilter to the prediction block to generate a filtered prediction blockfor the current block, wherein applying the bilateral filter comprisesdetermining weighting values to apply to neighboring pixels to a currentpixel of the prediction block to be filtered according to values of theneighboring pixels; and coding the current block using the filteredprediction block.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of coding video data, the methodcomprising: generating a prediction block for a current block of videodata; applying a bilateral filter to the prediction block to generate afiltered prediction block for the current block, wherein applying thebilateral filter comprises determining weighting values to apply toneighboring pixels to a current pixel of the prediction block to befiltered according to values of the neighboring pixels; and coding thecurrent block using the filtered prediction block.
 2. The method ofclaim 1, wherein coding the current block comprises: subtracting thefiltered prediction block from the current block to form a residualblock for the current block; applying a transform to the residual blockto generate a block of transform coefficients; quantizing the transformcoefficients to form quantized transform coefficients; and entropyencoding the quantized transform coefficients.
 3. The method of claim 1,wherein coding the current block comprises: entropy decoding quantizedtransform coefficients for the current block; inverse quantizing thequantized transform coefficients to generate transform coefficients forthe current block; inverse transforming the transform coefficients toreproduce a residual block for the current block; and combining theresidual block with the filtered prediction block to decode the currentblock.
 4. The method of claim 1, wherein generating the prediction blockcomprises: generating a first temporary prediction block according to afirst set of motion information for the current block; generating asecond temporary prediction block according to a second set of motioninformation for the current block; and combining the first temporaryprediction block with the second temporary prediction block to generatethe prediction block.
 5. The method of claim 4, further comprisinggenerating the first set of motion information and the second set ofmotion information according to bi-prediction.
 6. The method of claim 4,further comprising generating the first set of motion information andthe second set of motion information according to multi-hypothesisprediction.
 7. The method of claim 1, wherein generating the predictionblock and applying the bilateral filter to the prediction blockcomprises: generating a first temporary prediction block according to afirst set of motion information for the current block; bilateralfiltering the first temporary prediction block to generate a firsttemporary filtered prediction block; generating a second temporaryprediction block according to a second set of motion information for thecurrent block; bilateral filtering the second temporary prediction blockto generate a second temporary filtered prediction block; and combiningthe first temporary filtered prediction block with the second temporaryfiltered prediction block to generate the prediction block.
 8. Themethod of claim 7, further comprising generating the first set of motioninformation and the second set of motion information according tobi-prediction.
 9. The method of claim 7, further comprising generatingthe first set of motion information and the second set of motioninformation according to multi-hypothesis prediction.
 10. The method ofclaim 7, wherein combining the first temporary filtered prediction blockwith the second temporary filtered prediction block comprises averagingthe first temporary filtered prediction block with the second temporaryfiltered prediction block.
 11. The method of claim 7, wherein combiningthe first temporary filtered prediction block with the second temporaryfiltered prediction block comprises applying a first weight to the firsttemporary filtered prediction block and applying a second weight to thesecond temporary filtered prediction block.
 12. The method of claim 7,wherein combining the first temporary filtered prediction block with thesecond temporary filtered prediction block comprises generating theprediction block according to (M*P0+N*P1)/(M+N), wherein i in Pi denotesthe filtered temporary prediction block from reference picture list i (ibeing 0 or 1), M denotes a linear weight for the first temporaryfiltered prediction block, and N denotes a linear weight for the secondtemporary filtered prediction block.
 13. The method of claim 1, whereingenerating the prediction block comprises generating the predictionblock according to at least one of inter-prediction, intra-prediction,intra-block copy, cross-component linear model prediction, inter-layerprediction in scalable video coding, or inter-view prediction in3D-video coding.
 14. The method of claim 1, further comprising coding aflag for the current block indicating whether bilateral filtering isenabled.
 15. The method of claim 1, further comprising coding one ormore flags for one or more prediction blocks of the current blockindicating whether bilateral filtering is enabled for the correspondingprediction blocks.
 16. The method of claim 1, further comprising codingbilateral filter parameters for the current block.
 17. The method ofclaim 1, further comprising deriving one or more bilateral filterparameters without coding the derived bilateral filter parameters. 18.The method of claim 1, further comprising determining whether bilateralfilter parameters are to be derived or coded according to informationindicating whether motion information for the current block is codedaccording to advanced motion vector prediction (AMVP) mode or mergemode.
 19. The method of claim 1, wherein the current block comprises aluminance (luma) block, the method further comprising avoiding bilateralfiltering of prediction blocks for one or more chrominance (chroma)blocks corresponding to the luma block.
 20. The method of claim 1,wherein the current block comprises a block having a size less than athreshold, the method further comprising avoiding bilateral filtering ofprediction blocks for blocks having sizes greater than or equal to thethreshold.
 21. The method of claim 1, wherein the current blockcomprises a block having a predetermined shape, the method furthercomprising avoiding bilateral filtering of prediction blocks for blockshaving shapes other than the predetermined shape.
 22. The method ofclaim 1, wherein applying the bilateral filter to the prediction blockcomprises applying the bilateral filter to the prediction block afterdetermining that the current block is not predicted according to one ormore predetermined prediction modes.
 23. The method of claim 1, whereinapplying the bilateral filter to the prediction block comprises applyingthe bilateral filter to the prediction block after determining that aquantization parameter for the current block is below a threshold. 24.The method of claim 1, wherein applying the bilateral filter to theprediction block comprises applying the bilateral filter to theprediction block after determining that a quantization parameter for thecurrent block is above a threshold.
 25. The method of claim 1, whereinapplying the bilateral filter to the prediction block comprises applyingthe bilateral filter to the prediction block after determining that anumber of non-zero coefficients of the current block is less than orequal to a threshold.
 26. The method of claim 1, wherein applying thebilateral filter to the prediction block comprises applying thebilateral filter to the prediction block after determining that allabsolute values for each non-zero transform coefficient of the currentblock are less than or equal to a threshold.
 27. The method of claim 1,further comprising coding data representing one or more default sets ofbilateral filter parameters in at least one of a sequence parameter set,a picture parameter set, a video parameter set, or a slice header.
 28. Adevice for coding video data, the device comprising: a memory configuredto store video data; and one or more processors comprising circuitry andconfigured to: generate a prediction block for a current block of videodata; apply a bilateral filter to the prediction block to generate afiltered prediction block for the current block, wherein to apply thebilateral filter, the processor is configured to determine weightingvalues to apply to neighboring pixels to a current pixel of theprediction block to be filtered according to values of the neighboringpixels; and code the current block using the filtered prediction block.29. A device for coding video data, the device comprising: means forgenerating a prediction block for a current block of video data; meansfor applying a bilateral filter to the prediction block to generate afiltered prediction block for the current block, wherein the means forapplying the bilateral filter comprises means for determining weightingvalues to apply to neighboring pixels to a current pixel of theprediction block to be filtered according to values of the neighboringpixels; and means for coding the current block using the filteredprediction block.
 30. A non-transitory computer-readable storage mediumhaving stored thereon instructions that, when executed, cause one ormore processors to: generate a prediction block for a current block ofvideo data; apply a bilateral filter to the prediction block to generatea filtered prediction block for the current block, wherein theinstructions that cause the processor to apply the bilateral filtercomprise instructions that cause the processor to determine weightingvalues to apply to neighboring pixels to a current pixel of theprediction block to be filtered according to values of the neighboringpixels; and code the current block using the filtered prediction block.